Convertibles require a soft-top design so that they can fold backwards, and soft tops require careful cleaning from time to time. They are normally made of fabric or vinyl and can be subject to mould growth if they get wet and don't adequately dry out. Removing mould from a convertible top is not difficult but it should be done carefully.
Move the car into a shaded area. Water will evaporate faster in direct sunlight and you want to give cleaning agents a chance to work before they dry.
Spray the mould stains with a mixture of warm water and white vinegar. Use a half and half solution because the water helps prevent the acidity of the vinegar from damaging the convertible top. White vinegar is very useful for removing mould.
Scrub the mould away with a damp scrubbing sponge or a soft scrubbing brush.
If mould remains, wash the convertible top with warm water and a mild washing-up liquid. With the vinegar already breaking up the mould, the water and detergent should flush it away completely.
Dry the top completely before folding it back to help prevent further mould growth.